Heavy duty off-highway trucks utilized in mining and other excavating operations often are propelled by electric motors contained within a pair or more of the wheels of the vehicle. Electricity for the motors is usually provided by a diesel engine driven alternator, or generator, also on board the vehicle Vehicles thus propelled are very powerful, rugged and yet easily controlled by an operator.
The environment of the off-highway haulage truck is difficult. The trucks are subjected to severe strains as they are loaded and unloaded and collisions with loading rigs and equipment and other obstacles are not uncommon. These trucks encounter severe dust conditions and often have debris rained on them. And, of course, they operate outdoors so they are subjected to precipitation.
Electric motors must be ventilated to carry away heat generated therein. Thus, there must be a path for cooling air to exit the motor to the atmosphere. With wheel motors this exit path is generally through the hub region of the wheel of the vehicle. Any path open to the flow of cooling air is a potential path for debris and other foreign material, such as dust and water, to enter the motor. Such entry is obviously undesirable, so it is common practice to provide a cover over the cooling air exit of the wheel motor. In the past these covers have been fabricated from metal or rigid plastic materials and held in place by various means, such as detachable clasps. Despite these covers being constructed to possess great strength, they have invariably been damaged, dislodged and destroyed in the difficult environment of the off-highway truck. As a result, motor covers of prior designs have been the cause of costly maintenance problems for operators of the trucks. Because it was often not possible to repair damage to these prior covers, replacements had to be procured from the manufacturer. Any delay in obtaining a replacement cover resulted in down time on very expensive equipment.